M42 - What am I doing wrong?

[rodrigol]

Hi,

Last night the skies cleared in Essex and so I decided to couple my D7200 to a C11 again. I've been using recently this setup quite successfully for making moon mosaics. The seeing is not good at all these days so I've totally dropped the ball on planets. However, I decided to try for M42 core - trapezium region and managed to get a  few 30s exposures (unguided), which I tried stacked using DeepSkyStacker. The exposures where taken in RAW(NEF) format and seem to stack reasonably well - not perfect as there are still many adjustments I need to make to get the tracking acceptable. I know a C11 is not the ideal setup for this so please bear with me. All the original exposures show some decent amount of colour (please see below). However, the stacked TIFF is mostly grey. Please, what am I doing wrong?

 

[PeterCPC]

When you have stacked in DSS are you adjusting the saturation slider? It should be set to around 25%.

Peter

[Robp]

Have you got anything weird set in the Raw/FITS DDP settings section?

[rodrigol]

Thanks for answering. I did check the saturation slider in DSS but got nowhere, even small increment in small steps. I should have mentioned this in my posting; but then, I've been trying lots of things but simply can't recover the colour.

In relation to RAW/FITS DDP settings - I didn't touch any settings here. Maybe you can clarify what 'weird' would be here?

Thanks!

 

[Oddsocks]

If your Nikon is one of the latest models then the built-in DCRaw module used in the primary release version of DSS, version 3.3.2 may not be able to decode the bayer matrix correctly.

On the DSS download page look for the link to the latest version of DSS, it is currently version 3.3.4.

http://deepskystacker.free.fr/english/index.html

Delete the old DSS folder completely from your system and then download and decompress the 3.3.4. version and try again, the 3.3.4. version is a RAR compressed file so you may need a RAR decompressor such as Frog (free) RAR opener if you have nothing on your pc that can decompress RAR files natively.

http://www.philippwinterberg.com/software/free_rar_extract_frog.php

Don't forget to virus scan any download linked from this post before opening it....

[Oddsocks]

This is the "default" setting for raw files in DSS:

 

[rodrigol]

Many thanks for the tips and time to answer! I watched and double check software versions and possible in-camera NEF settings and options and report back. 

[wxsatuser]

The stacked image will be dark and lack colour.
You might be able to make it slightly better by having 'Use per channel background calibration' enabled in recommended settings.

If you got the colour out of a single exposure you should be able to do it with the stack.

Here is an example, an Autosave tif of Orion's head SH2-264, quite dark and lacking colour.
The resultant image after post is below it.

 

 

 

[rodrigol]

Wow! Mike: That is very impressive. I'm a newb at this but seeing your work is inspiring :-)

 

[rodrigol]

I think I made some progress. The autosave images seem to have been save with wrong colour depth but I don't understand how or why. Once I converted them from 32 to 16 bits I could do further work using PS and YES - the colours are there. 

Thanks to everyone for you helpful tips!

 

[Oddsocks]

I had a quick look at your posted "monochrome" image this afternoon using PixInsight and it does have some colour but almost non-existent, the good news is that the colour that is there is correct so DSS is using the right debayer protocol for your camera.

It is normal for stacked RAW images to come out of DSS showing very little colour and you have to adjust the saturation slider up to round 25% and remember to click "apply" otherwise nothing happens!

I did wonder if you had been moving the saturation slider but not clicking the apply button???

After stacking, in the picture module, adjust the middle slider in the RGB/K tab so that the histogram peak passes below the centre of the curve as in the picture, small changes to the slider have to followed up by clicking the apply button each time, until the picture has the tonal range you are after.

 

Then, move to the saturation tab and adjust the saturation slider to 25% and apply, make any small changes you require to adjust the saturation level and apply after each adjustment, then save the image and make the final corrections in Photoshop or Gimp etc.

 

Photoshop does not allow you to use all the processing tools in 32 bit mode so once the image is imported and opened in PS change to 16 bit mode and you will be ok.

 

[wxsatuser]

6 hours ago, rodrigol said:

I think I made some progress. The autosave images seem to have been save with wrong colour depth but I don't understand how or why. Once I converted them from 32 to 16 bits I could do further work using PS and YES - the colours are there. 

Thanks to everyone for you helpful tips!

 

Thats correct, the Autosave tiff is 32bit.

Pixinsight can deal with these but PS needs 16bit to get the full range of tools to work.

[rodrigol]

Gosh! Indeed a little adventure in photo processing and I want to thank you all for all your help, tips and setting me in the path of wizdom. Below is the processed image after converting to 16 bits and doing some small adjustments such as levels and saturation. I now wish the  cgem dx was tracking better to avoid the weird star shapes. Once again I could not have done this without you guys!

 

 

[ollypenrice]

Want a dodgy, unethical fix for star shapes which I would never dream of using myself? (Ahem. )

Photoshop. Use magic wand to select a star and then record this action and save to a function key:

Select, modify, expand (try 4)

Select, modify, feather (try 3)

Filter, Blur, radial blur, set to best quality and spin.

Deselect. (Don't forget this.)

Stop recording.

The values for expand and feather will vary with pixel size and it can be an idea to have two versions recorded, one for large stars and one for small. To use the actions just click on a star and press the funtion key.

 

[happy-kat]

Are your stars always looking like little triangles?

 

[rodrigol]

Wow Olly! Is it 'unethical' if it helps clarify an issue by removing an artifact of the instrumentation? I need to try your action and will let you guys know the result. 

Happy-kat: The stars in these series came out like little triangles, yes. I'm putting it to tracking issues but have yet to confirm. It's the first time I took this type of shot with the equipment mentioned so I've got nothing to compare at the moment.

[happy-kat]

It is just camera and c11, there are no filters or any other glass is use?

[rodrigol]

Hi Happy-Kat,

 

Yes, it is only the C11 + Moonlight SCT focuser + D7200 in the OT. Maybe weird stars are due to lack of a FR/FF?

 

 

 

[Oddsocks]

On 29 February 2016 at 09:19, rodrigol said:

Maybe weird stars are due to lack of a FR/FF?

 

 

 

In this case the problem star shape is mostly tracking issues, during the exposure the stars are occupying three distinct overlapping positions and the result is the stars become triangular.

A flattener will only remove coma which will be most evident at the edges of the image, not the centre.

Most likely this is backlash in the RA and DEC gears and it is common to see triangular or "L" shaped stars where the mount is "bouncing" backwards and forwards between the teeth of the drive gears.

When you set up the mount do not try to achieve a perfect balance, try to leave the equivalent of 0.5kg to 1kg unbalanced in both RA and DEC, as long as the OTA is lying well to either side of the meridian then the mount gears will be biased to engage on one side only and the backlash should all but disappear giving you round stars again.

When the OTA is close to the meridian the offset weights in RA will not have such a positive effect and a cheap solution is to tie one end of a 2 metre length of 6mm diameter elastic shock cord to the counter weight arm or OTA and the other end to something heavy on the ground or one of the tripod legs, then shorten the cord to produce a pull equivalent in the range of 0.5kg to 1kg, this will produce a steady off-balance force the same as having the main weights out of balance but it is less effected by the OTA getting close to the meridian, only watch out not to fall over the elastic cord in the dark and untie it before slewing off to a new target.

Elastic shock cord can be found sold by the metre in yacht chandlers or DIY stores.

When you attach your camera try to align the sensor so that the long, or short, edge is aligned with the RA axis that way when you analyse the image you will be able to tell which axis has the problem backlash, or how much is being contributed from both axis.

 

 

[rodrigol]

Dear  Olly,

This is excellent advice! As a learner, this is a great lesson to receive. I though very good balance was the key to all guiding matters. I'm always weary of damaging gears and motors but what are saying makes perfect sense. Perfect balance and perfect tracking do not go together :-)

Thanks!